1. Technical Field
The present disclosure relates generally to mobile communications, and more particularly, to a method and system for resource sharing between demodulating paths of a rake receiver. In general, a rake receiver combines signals that are transmitted on a channel in different paths from a transmitter and arrive at different time points in order to increase reception performance through path diversity.
2. Background of the Related Art
As shown in FIGS. 1 and 2, a conventional rake receiver 100 includes an RF analog subsystem block 102, which converts signals received from an antenna 104 to digital data and feeds the converted digital data to each finger 1061–106N. In each finger 1061–106N, symbols transmitted from the transmitter are demodulated by PN despreading blocks 1081–108N.
The demodulated symbols Wi and the estimated pilot channel gains Pi are provided by Walsh decovering blocks 1101–110N and pilot filter blocks 1111–111N, and they are transferred to channel estimation and phase distortion compensation blocks 1121–112N. The recovered symbols Si are stored in a kind of FIFO memory within time deskew buffers 1141–114N respectively. A symbol combiner 116 reads the symbols from the time deskew buffers 1141–114N (four time deskew buffers are shown in FIG. 2) of the fingers at the same time, combines them, and sends the symbols to a long code descrambler 118 for combining the symbols with a long code. A power-bit extractor 120 is connected to each time deskew buffer 1141–114N and to the symbol combiner 116.
In FIG. 2, reference characters A, B, C and D denote symbol data stored in time deskew buffers 1141, 1142, 1143, and 114N of the rake receiver 100. The symbols are numbered to represent their sequence numbers. The pluralities of demodulating fingers 1061–106N operate in the same manner to demodulate signals with different arrival times. Therefore, the hardware of each finger 1061–106N has the same structure.
Each demodulating finger 1061–106N in the rake receiver 100 demodulates the symbols independently in a temporal sense, and stores the demodulated symbols in the time deskew buffers 1141–114N. That is, since symbol combination can be performed by the symbol combiner 116 only after demodulation of the symbols of each finger 1061–106N, the time deskew buffers 1141–114N store previously demodulated symbols until a symbol from the last branch is demodulated. Finally, all the symbols stored in the time deskew buffers 1141–114N are combined in the symbol combiner 116. In order to enable each finger to operate in its own timing reference, an independent time deskew buffer with the same size as the time deskew buffers 1141–114N is provided for each finger 1061–106N.
For example, the required size of a time deskew buffer for one of RC3, 4 and 5 modes of a CDMA2000 system is (FCH_FIFO_DEPTH+SCH_FIFO_DEPTH+DCCH_FIFO_DEPTH+PILOT_ENERGY_FIFO_DEPTH)×DATA_WIDTH×number of fingers. Thus, the depth of the FIFO memory for storing data is increased and the architecture or structure of the rake receiver for third high data rate communications systems becomes complex.
In third generation systems, such as CDMA2000 and UMTS, or other high data rate communications systems, the required depths of the FIFOs are remarkably increased since more symbols are to be stored for higher data rate. In addition, the number of fingers is increased since more fingers are necessary to facilitate soft hand-offs and enhance multi-path diversity effects. The fact that an independent time deskew buffer of the same size as the time deskew buffers 1141–114N must be provided for each finger 1061–106N, thereby causes an increase in the size of the FIFO memory, or time deskew buffers 1141–114N, in proportion to the number of fingers 1061–106N. Hence, there is an increase in the size and complexity of the rake receiver.
Accordingly, a need exists for a rake receiver for high data rate communications systems that is able to share resources between demodulating branches without using independent hardware resources, i.e., such as an independent time deskew buffer of the same size as the time deskew buffers 1141–114N for each finger 1061–106N, to thereby reduce the area and complexity of the rake receiver.